Dentistry

Description

Dentistry

Dentistry (Lat. dens, tooth), the surgical treatment of the teeth, and the manufacture and fitting of artificial teeth. Although it is only within less than a century that dentistry has taken the rank of a distinct profession, attention was directed from the earliest periods to the means of preserving and improving the beauty of the teeth. In the time of Herodotus dentistry appears to have been practised in Egypt as a distinct branch of surgery, as was also the treatment of the diseases of the eye and of the ear. Little, however, is known of the attainments of these early practitioners. In the ancient tombs of this people artificial teeth of ivory or wood were found by Belzoni and others, some of which were fastened upon gold plates. It is also stated that teeth of the mummies have been found filled with gold. Thus it would seem that the ancient Egyptians understood processes of the art which are commonly regarded only as inventions of modern times. Artificial teeth are alluded to by several of the Greek and Latin poets, as Ovid, Martial, and Horace. The works of Galen, written in the 2d century, contain the earliest treatises upon this subject, and they continued to be the best until the works of Fallopius, Eustachius, and Ambroiso Pare appeared in the 16th century.

During the 18th century the attention of many medical men in France and England was directed to the subject, and a number of elaborate works were published devoted exclusively to the art of dentistry. These, and prominently among them the treatise of John Hunter (1771-'8), laid the foundation of the English school of dentistry. The subject, however, was treated anatomically and philosophically rather than practically; and the same may be said of the writings of the eminent French surgeon of this period, Bichat. Neither of these was a practical dentist, and the subsequent publications of Dr. Blake in 1798, and of Fox in 1803 and 1800, as of others at later dates, served rather to elucidate the physiology of the teeth and the nature of the diseases to which they are subject than the method of treating them. From advertisements in the newspapers of 1803 the practice of making teeth and cleaning them appears to have been in the hands of silversmiths or jewellers. In 1820 the " Principles of Dental Surgery," by Leonard Koecker, M. I)., who had practised dentistry from 1807 to 1822 in Baltimore and Philadelphia, appeared in London, and fully established the claims of the art to take rank as a distinct branch of science. From that time new treatises have continued frequently to appear.

The progress of the French school was very rapid in the early part of the present century. Prof. Baumes's treatise on first dentition and the diseases that accompany it appeared in 1805, and about the same time a work on the theory and practice of the art by Laforgue. A number of works were published by Delabarre between 1815 and 1826 on different subjects relating to the teeth and their treatment. Among them is a treatise on "Mechanical Dentistry," published in 1820, and illustrated with 42 plates.

It was during this period, when publications upon dentistry were frequently appearing in France, that the manufacture of artificial teeth of porcelain was introduced; and in 1821 a work upon this subject was published by Audi-bran, entitled Essai historique et pratique sur les dents artificielles incorruptibles. By this it appears that Fauchard in 1728 proposed their manufacture; and that in 1770 Duchateau, a chemist of St. Germain-en-Laye, attempted to produce them, and finally succeeded with the aid of Dubois, a dentist of note in Paris. The latter imitated the colors of the natural teeth and gums by the use of mineral oxides, and obtained royal letters patent for the invention. Dentistry was introduced into the United States by Le Mair, of the French forces which joined our army during the revolutionary war. An Englishman named Whitlock also commenced the practice soon after the arrival of Le Mair. About 1788 John Greenwood established himself in New York, the first American of this profession. In 1790, and again in 1795, he carved in ivory an entire set of teeth for Gen. "Washington. They were secured by spiral springs, and the neatness and ingenuity of the work was considered equal to any executed at that period abroad.

Other dentists soon appeared in New York, Philadelphia, and Baltimore. Their work included the extracting of teeth, filing and cleaning them, and replacing the natural teeth when lost with artificial ones, commonly made of ivory. Dr. Hudson, formerly of Dublin, who had settled in Philadelphia, first directed his attention particularly to the cure of the diseases of the teeth, and to arresting the progress of dental caries. In 1820 the number of practitioners in the United States was probably little more than 100. Ten years afterward there were about 300, of whom probably not more than one sixth were well instructed. But the increase in their numbers was afterward very rapid. In 1842 they were believed to number about 1,400, and in 1872 about 5,000. An important event in the history of dental surgery in this country was the establishment of the "American Journal and Library of Dental Science" in Baltimore, in 1839. The society of dental surgeons was soon after formed, and at its second annual meeting the "Journal" was made the property and organ of the association.

Maryland founded by its legislature, a few months previous to the organization of the society above named, a college of dental surgery, with four professorships, designed for instruction in the principles and mechanical practice of the art. Two years afterward another society of dentists, like that of Baltimore, was organized at Richmond, Va., and in August, 1844, a third was formed at Cincinnati, Ohio, styled the "Mississippi Valley Association of Dental Surgeons." A college of dentistry has also been established in Philadelphia and another in Cincinnati, and state and local dental societies in various parts of the country. In August, 1855, the national convention of dentists was organized through the active exertions of Dr. Elisha Townsend of Philadelphia, and its first annual meeting was held in that city. Dr. John B. Rich of New York was its first president. Besides the reports of these societies, which have disseminated a knowledge of the discoveries and improvements made in the science, many very valuable works of a practical nature have been published by American authors. - The means of preventing the diseases to which the teeth are subject, is a branch of dental science quite as important as that relating to the arrest and cure of these diseases.

These means consist, first, in giving what assistance nature requires to bring the teeth of second dentition into a regular arrangement; and secondly, in the care of the individual himself in preserving the teeth uniformly clean. As the temporary or first set of teeth drop out, which as a general rule they should be allowed to do, by their roots being absorbed, the second set already formed succeed and take their places. Of the temporary teeth there are but 20, and these are of small size. The teeth of the second dentition are 32 in number, with one or two exceptions are of larger size than their predecessors, and consequently occupy a greater space. Yet these, appearing one by one, take their places, and should occupy in the harmonious process of the growth of all the parts the same room apparently that was filled by the 20 deciduous teeth. This is accomplished by the elongation forward of the jaw, the arch gradually assuming the form of a semi-ellipse in place of that of a semi-circle. Teeth irregularly arranged, interfering with each other, or as in some cases with the lips, or pointing inward so as to be removed from the healthy action of mastication, or twisted in their sockets, are not only disfiguring, but are particularly liable to disease and decay.

From their first appearance to the age of 16 of the individual, they may be treated by various mechanical applications attached to the other teeth and bearing suitably upon those to be brought into place, so that without violence the work of nature is gently assisted, and a perfect set is gradually formed. It is the opinion of dentists that when the teeth are kept perfectly clean they will not be affected by caries. As the secretions of the mouth are, however, liable to be vitiated by constitutional disorders, the keeping them clean requires great vigilance. When caries occurs it should be immediately removed by the use of the file. The surface of the bone from which the enamel is removed should be left smooth and polished, and if proper care be afterward taken in keeping it clean, the disease may not return. If the decay has extended into the bony substance of the tooth, the filing is then only preparatory to the complete removal of the diseased portion by excavating with suitable instruments, and filling the cavity with some proper material.

Much attention was formerly given to shaping the cavity, in order that by its contracted aperture the filling should be held in as by dovetailing; but by the use of gold foil and sponge gold specially prepared for this purpose, it is now found practicable to apply the metal in successive portions, and build up a solid block of any shape by incorporating each portion with that which preceded it. This is done by carefully packing it with suitable instruments, and the gold may be thus rendered so compact, it is affirmed, that its specific gravity shall equal that of the cast metal. In wide-mouthed cavities the filling is secured by being built upon plugging carefully introduced into the cavities of the roots, and also by lateral pins of the gold filling made to enter from this into little holes or grooves drilled for the purpose into the walls of the tooth. It has been generally considered impracticable to preserve a tooth when the decay has reached into the internal or pulp cavity. In this condition inflammation often takes place at the root, and matter collects, forming an ulcer between the periosteum of the tooth and the bone.

If the discharge of this be stopped by filling the cavity, the matter will find its way through the gum, causing a gum boil near the root; or it produces inflammation of the face, often attended with great suffering, which is relieved only by the removal of the tooth. The modern treatment is to perforate the sac at the root by a fine drill passed through the cavity; and if the pulp be sensitive, it is cut out and removed by a delicate steel wire furnished with a hook at the end, so small that it can pass freely into the nerve cavity. A solution of creosote or carbolic acid is then injected into the cavity, and as soon as a healthy action has taken place the tooth may be safely filled, with the liability of further trouble from the same cause greatly reduced. - The only unobjectionable material for filling teeth is gold foil or the sponge gold specially prepared for this purpose. The latter material is produced by dissolving gold free from copper in nitro-hydrochloric acid, placing the solution in a fiat-bottomed vessel, and heating and precipitating by strong solution of oxalic acid. In a few hours the gold is wholly deposited, and the supernatant liquid may be decanted off, taking care not to disturb the gold at the bottom.

The vessel is then several times filled with boiling water and decanted, until the last washings contain no more oxalic acid. The gold is now carefully slipped upon a piece of filtering paper, and by means of a spatula gently pressed into the form of the desired cake, but a little thicker. It is then removed to a porcelain crucible, and heated for a short time, somewhat below a red heat, when it shrinks and becomes coherent. Tin foil may be used, and its malleability and cheapness well adapt it for large and badly shaped cavities and for temporary fillings in sensitive teeth; but it is liable to oxidize and produce discoloration. Temporary fillings, for the purpose of protecting the cavity while it is being prepared for gold filling, are often made of gutta percha. A preparation of it known as Hill's stopping, made by incorporating with it a powder made of quicklime, quartz, and feldspar, is highly recommended. When this composition is used a condensing instrument large enough to cover the filling should be held upon it until the nerve becomes cool. A mixture of chloride and oxide of zinc, called oxychlo-ride of zinc, or os artificiel, has lately been much used as a temporary filling, and also for pulp cavities.

Exposed nerves have also been covered with it, and gold used to complete the filling. The operations for filling teeth are varied and complicated. Many ingenious machines have been lately introduced for preparing cavities and condensing the filling. Drills worked by treadles, and also by galvanism as a motor force, and automatic mallets have been successfully applied. - The extraction of the teeth is an important branch of dental practice; safe and easy with good instruments in skilful hands, but, as practised by the unprofessional operator, not a little hazardous. The improved instruments of modern times, however, have greatly lessened this risk, and pain is avoided by the use of anaesthetic agents. - The last department of dentistry to be noticed is the construction and application of artificial teeth. These were formerly carved from ivory of the tusk of the elephant or the tooth of the hippopotamus. They were obtained also by altering the shape of the teeth of some of the inferior animals; and the crowns of human teeth were often conveniently engrafted upon the roots of the original front teeth.

All these materials are objectionable from their susceptibility to the action of the fluids of the mouth; ivory soon becomes offensive from being saturated with these fluids; and all of them are liable to decay, inducing at the same time disease in the sound teeth remaining. Porcelain teeth perfectly resist the corrosive action of the fluids of the mouth, and imitate so perfectly in color and animated appearance the natural teeth, that they are often not easily distinguished from them. Various methods of securing artificial teeth in their places have been in use. So long ago as 400 years B. C. they were fastened by ligatures of flax or silk, and with wire of gold or silver, to the natural teeth that remained. In modern times metallic clasps, spiral springs, and fastenings of gutta percha and of caoutchouc have been used for this purpose; but the most perfect method is to secure the teeth, either in whole Or partial sets, to a plate of gold or other metal, which is so accurately fitted to the gums that it is firmly retained by atmospheric pressure. In making an artificial set of teeth, the first object is to obtain in some hard metal an exact model of the mouth in which the plate is to be fitted.

For this purpose, yellow or white wax, free from mixture of grease, and softened by warm water, is placed in a shallow vessel, which may he introduced into the mouth. Plaster of Paris made into paste may he substituted for the wax. The contents of the cup are firmly pressed around the gums, and, if for the upper jaw, are made to cover the roof of the mouth as well. An experienced operator thus obtains in a few minutes an exact mould of the parts to which the material is applied. The teeth, if any are present, leave their forms faithfully impressed in their true positions, and the cavities between are represented by corresponding projections in the wax or hardened plaster. The impression removed from the mouth serves to furnish a model of the jaw, which may be taken in plaster of Paris also. This is used as a pattern in moulding sand, and a cast is then obtained in any metal, as for instance zinc; and by pouring melted lead upon the zinc, which is turned over upon its face and surrounded with a brass or iron collar for retaining the lead, a mould in this metal is obtained precisely like the original one in wax.

By means of the zinc cast and lead mould, the exact shape of the parts is transferred to the sheet of gold or other metal, this being placed between the two, and made, by hammering and swaging, to assume all their irregularities of surface. The fit is the more readily made if the teeth have been cut off from the plaster model before making the metallic casts. A duplicate plaster cast serves to give the position of those teeth to which the plate is to be finally fitted. - A variety of materials have been experimented upon, in which to securely imbed the bases of the teeth. Gutta percha has been used to contain them; but its texture and strength were in a short time destroyed by the action of the fluids of the mouth. It was then applied vulcanized or mixed with sulphur; and caoutchouc is employed in the same way. These prove to be important auxiliaries in mechanical dentistry, especially for temporary sets of teeth. They do not, however, readily take the colors which may be applied to more suitable substances. In 1851 the process called continuous gum was invented by Dr. John Allen, professor in the Ohio college of dental surgery.

In this a sili-cious compound, similar in composition to that of which the teeth are made, but more fusible, is applied in the form of a paste over the fastenings at the back of the teeth, and also in the front, so as entirely to bury the ends of the teeth, as the natural ones are buried in the gums. To withstand the high degree of heat requisite for baking this upon the plate, platinum is substituted for gold. Platinum has besides the advantage of forming at a high heat a close union with the silicious compound, which is spread over the lingual side of the plate as well as over the bases of the teeth. When thoroughly dry, the work is baked at a white heat in the muffle of an assaying furnace. A new application of the paste is then made to fill all the crevices caused by shrinking, and upon this coating are made numerous ridges and depressions with the spatula, which, when afterward covered with the coloring enamel, cause this to assume different shades of the color, and present the appearance of the natural gums. The baking is repeated, and after this the coating of coloring matter, called the gum enamel, is applied, when a third baking completes the process, by which a proper degree of hardness and a natural color are produced.

The compositions used are empirical mixtures of pure silica and feldspar, with a suitable flux to produce a fusible compound, possessing sufficient strength, hardness, and permanency of character. The work can easily be repaired when broken, or alterations made when required by changes in the mouth, by building upon it more of the paste and again baking; in this way even the length of the artificial teeth can be increased and new ones introduced. In the same way the artificial processes called cheek restorers were applied by Dr. Allen, which are projecting portions built upon the artificial gums far back in the mouth, and serve to distend the cheeks when these are fallen in. The mechanical operations connected with the work have led to increased knowledge in the use of plastic compounds, and introduced improved methods of treating the metals employed.